Many modern motor vehicles are equipped with automatic headlamp light control systems. These systems utilize an ambient light sensor to automatically switch the headlamps “ON” in nighttime and in low-light driving conditions, and turn them “OFF” or dim the headlamps in brighter conditions. These systems eliminate the need for the driver to manually control the headlamps. The ambient light sensor provides an output signal related to the ambient light level and creates a headlamp “ON” threshold of ambient lighting condition. Thus, when the vehicle equipped with such a system experiences the transition between daytime and nighttime driving conditions, and visa versa, the headlamps are activated and deactivated (or dimmed) when the threshold is crossed.
In addition to forward lighting requirements, ambient lighting conditions also affect instrument panel lighting requirements. In order to provide acceptable contrast for reading instrument panel gauges and indicators, instrument panel lighting is generally provided both in daytime and in nighttime driving conditions. Due to the bright ambient light conditions of daytime driving, the illumination level for instrument panel lighting is greater in daytime as compared with nighttime driving conditions. In vehicles equipped with automatic headlamp control systems, once the headlamps are turned “ON”, the instrument panel illumination is changed by the vehicle lighting system in a step manner to a lower intensity. A lower intensity instrument panel illumination is required at nighttime since ambient lighting conditions are low and excessive brightness of instrument panel lighting would be a distraction and a glare hazard. Instrument panel lighting circuits typically incorporate a manual illumination control, allowing the driver to adjust the level of intensity, especially usable in nighttime driving conditions.
In addition to variable intensity instrument panel lighting, many vehicles incorporate navigation systems, typically having a flat panel display such as an LCD type, having a contrast control and/or display brightness control. The display settings are also typically automatically changed between daytime and nighttime driving condition in response to the headlamp “ON” and “OFF” (or dim) control signals.
In presently available ambient light based illumination control systems, the illumination levels of the instrument panel and, if equipped, the navigation display or other vehicle displays, are switched in a step function manner between daytime and nighttime driving conditions. Particularly when the vehicle driver has set a low illumination level for instrument panel lighting, the transition between headlight “ON” and “OFF” conditions can produce a condition in which instrument panel illumination is insufficient in the transition ambient lighting range. This results from the fact that automatic control of instrument panel illumination generally switches abruptly between two levels; a high level associated with daytime driving conditions, and a lower level for nighttime driving conditions which is set at the manual adjusted level as previously described.
The presently available systems thus do not provide optimal instrument panel illumination over the full range of ambient lighting conditions. This leads to the need for the operator to manually adjust panel illumination, which defeats the purpose of providing automatic control.